Generally, Gallium Nitride technologies are enabling fabrication of power field effect transistors (FETs) with lower gate capacitance (Cg) and gate charge (Qg), compared to state-of-the-art silicon FETS, such as metal oxide semiconductor FETs (MOSFETs) for a same resistance of a FET in saturation (rdson).
Currently Gallium Nitride FETs (GaN FETs) can be four to five times better than a MOSFET (i.e. these various values are ¼ to ⅕ that of silicon FETs), and it is believed than GaN FETS can be potentially 100s of times better than MOSFETs. This means that GaN FETs can be switched at a much higher switching frequency with an equivalent power loss. Equivalently, it means that GaN FETs can aid in reaching a higher efficiency in a power circuit, if the GaN FETs are used instead of MOSFETs without a change in operation frequency.
While GaN FETs have been available for some time, a recent breakthrough in their manufacturing in 2010 has resulted in GaN FETs implemented on silicon substrates, which has caused industry to believe that GaN FETs can be adopted instead of MOSFETs in at least a fraction of uses in the next few years.
For more information regarding GaN FETs, please see “Application Note: Fundamentals of Gallium Nitride Power Transistors” by Stephen L. Colino, et al, Efficient Power Conversion Corporation, Copyright 2011, which is hereby incorporated by reference in its entirety. Also, please see “Enhancement-Mode GaN MIS-HEMTs With n-GaN/i-AlN/n-GaN Triple Cap Layer and High-k Gate Dielectrics”, by M. Kanamura, et al, IEEE Electron Device Letters, Vol. 31. No. 3, March 2010, pages 189-191, which is also incorporated by reference in its entirety.
However, there are drawbacks associated with GaN FETs. Although GaN FETs have higher performance than silicon MOSFETs, they are also more sensitive and demanding in their usage requirements. One example of this sensitivity is that of the GaN FETs' gate and source (Vgs) sensitivity to voltage excursions. For example, efficient power conversion (EPC) enhancement-mode GaN FETs typically require a 5 Volt drive signal to achieve saturation, but the drive Voltage should not exceed 6 Volts under any condition, since it will cause a “soft damage” (increase of rdson) of the GaN FET. To make matters, worse, unlike silicon MOSFETs, GaN FETs do not have a body diode, and, therefore, when the GaN FETs are off, if Vds goes negative, a GaN FET turns on at −3 Volts or −4 Volts difference between drain and source, instead of a body diode drop voltage as would occur in the case of a MOSFET.
Therefore, there is a need in the art to address at least some of the issues associated with GaN FETs.